Phenol-contaminated water as a by-product of various chemical processes is a recognized industrial problem, both in terms of water toxicity and recovery of phenols. As to toxicity, it is known that phenols are toxic to fish at concentrations as low as 0.1 ppm, while at 0.01 ppm, an extremely disagreeable taste is imparted to water treated by hypochlorite to render it potable, owing to the formation of chlorophenols. Residual phenol concentrations from such sources as gasworks, coking plants, refineries, coal processing plants, tar processing plants, pesticide plants, phenol conversion plants, and phenoplast plastics materials plants vary from a few ppm to as high as 10%.
Known processes for the purification of phenolated water are few, and may be broadly characterized as falling into one of two categories: (1) recovery processes; or (2) chemical/biological destruction processes. In the first category, there are included processes such as liquid-liquid solvent extraction (see, for example, U.S. Pat. No. 3,673,070), steam distillation, absorption on activated charcoal or ion-exchange resins, and foaming with surfactants. In the second category are included processes such as treatment by activated sludges and bacterial beds, oxidation by ozone, permanganate, chlorine, catalayzed hydrogen peroxide, and electrolysis (see U.S. Pat. No. 3,730,864). Another process not falling into either category is that disclosed in U.S. Pat. No. 3,931,000, comprising passing an aqueous polysubstituted phenolic feed stream around the outside of a bundle of hollow fibers while passing sodium hydroxide solution into the hollow fibers, the phenols passing through the fibers to form insoluble sodium phenate salts which concentrate inside the hollow fiber membrane, and are swept out of the system with the sodium hydroxide solution stream.
However, none of the above processes have been totally effective, leaving a significant residual phenol content, and will suffer from various serious drawbacks, such as strict monitoring of the content and pH of the feed stream in the case of bacterial bed treatment, regeneration of absorbents, high cost of reactants in the case of oxidation treatment, and production of undesirable by-products (chlorophenols) in the case of chlorination treatment.
Use of membranes for pervaporation has been limited. The only known commercially useful pervaporation membrane is one for dehydrating ethanol and propanol which comprises a composite of polyvinyl alcohol on a porous support of polyacrylonitrile. See 53 Desalination 327 (1985). Ion-exchange membranes have been investigated as to pervaporation effects on aqueous ethanol and lower carboxylic acid mixtures, with the water having pervaporated preferentially. Boddeker, Proc. 1st. Int. Symp. Pervaporation (Feb. 1986). And silicone rubber membranes have been used for the selective pervaporation of halogenated hydrocarbons and butanol from aqueous solutions thereof. See 8 J. Membr. Sci. 177 (1983). However, none of these membranes have been incorporated into a pervaporation process that is technically feasible.
It is therefore a principal objective of the present invention to provide a simple, highly efficient, and inexpensive method of purifying phenol-contaminated water.
It is an equally important objective of the present invention to provide a simple, highly efficient and inexpensive method of recovering phenols from aqueous phenolic solutions.
These and other objects that will become apparent are achieved by the method of the present invention, which is summarized and described in detail below.